Thermal processing torches, such as plasma arc torches, are widely used in the heating, cutting, gouging and marking of materials. A plasma arc torch generally includes an electrode, a nozzle having a central exit orifice mounted within a torch body, electrical connections, passages for cooling, and passages for arc control fluids (e.g., plasma gas). Optionally, a swirl ring is employed to control fluid flow patterns in the plasma chamber formed between the electrode and the nozzle. In some torches, a retaining cap can be used to maintain the nozzle and/or swirl ring in the plasma arc torch. In operation, the torch produces a plasma arc, which is a constricted jet of an ionized gas with high temperature and sufficient momentum to assist with removal of molten metal.
A problem with existing plasma arc torches, including handheld plasma arc torches, is that they have difficulties flush cutting a workpiece having one or more internal corners due to the axial configuration of the torches. As shown in FIG. 1, a conventional plasma arc torch 100, which includes a rotational symmetric torch tip 102, cannot make a flush cut in the workpiece along the desired path 104. Specifically, the plasma arc torch 100 has difficulty cutting off the protruding flange 106 as close as possible against the horizontal surface 107 of the base 108 without cutting below the horizontal surface 107. Instead, the best cut achievable by the plasma arc torch 100 is indicated by the path 110. As a result, secondary operations, such as grinding, are required to remove the excess workpiece section 112 to achieve the desired flush cut 104. In addition, the closer the plasma arc torch 100 directs a plasma arc flow to the corner of the workpiece, the more likely the arc can inadvertently damage the base 108, such as extending the cut below the horizontal surface 107 of the base 108 along the path 114. Yet another limitation of the plasma arc torch 100 is its inability to ensure that a cut in a workpiece corner is consistently reproducible. For example, the plasma arc torch 100 does not have any positioning mechanism to ensure that the same cut can be made at the same relative location in the corners of different workpieces.
Another problem with existing plasma arc torches, including handheld plasma arc torches, is that they have difficulties cutting a workpiece at a precise bevel angle without the assistance of costly accessories. A bevel cut can be useful in many operations, such as in a welding preparation process for producing a beveled edge in a workpiece that is not perpendicular relative to the face of the workpiece. In general, making bevel cuts can be time-consuming and expensive if traditional welding and grinding methods are used.
As shown in FIG. 2, a conventional plasma arc torch (e.g., the torch 100 of FIG. 1) has difficulty cutting a path 154 in a workpiece 162 at a desired bevel angle 150 (e.g., 45 degrees) in relation to a longitudinal axis 152 that is perpendicular to a processing surface 164 of the workpiece 162. An operator can inadvertently tilt the torch 100 in either of the directions 156a and 156b, thereby altering the cut path 154 from the desired bevel angle 150 and impact the quality of the resulting bevel cut. The difficulty is exacerbated if the operator wants to use a template for the cut and/or maintain the same cut angle 150 over a cut distance 160 by dragging the torch 100 along the length 158 of the workpiece. Often, the resulting cut includes jagged edges that require secondary operations, such as grinding to smooth the surface of the cut piece and achieve the desired slope. In addition, the plasma arc torch 100 does not have any positioning mechanism to ensure that the same bevel cut can be made over the distance 160 in a single workpiece or in different workpieces to provide consistently reproducible results.